82 THE VOYAGE OF H.M.S. CHALLENGER. 



The deep-sea species of Serolis have a wider range to the north than the shallow-water 

 species, though as yet none have been obtained north of the equator; since there are only 

 four deep-sea species known, and, with the exception of Serolis hromleyana, only a small 

 number of specimens of each were dredged, it is perhaps rather premature to draw any 

 deductions from the facts, and the following notes must be accepted for what they are 

 worth. 



In the first place, it must be noted that in no case do any of the shallow-water species 

 pass the 300 fathom limit ; nor are any of the deep-sea species known to inhabit shallow 

 water ; the shallow-water are specifically distinct from the deep-sea forms. I may correct 

 here a misleading statement in Gerstaecker's account of the Isopoda in Bronn's 

 Thierreichs, from which it would appear that one species is common to " deep " and 

 "shallow" water; on p. 241 of the above quoted work, Gerstaecker gives a list of the 

 range in depth of the family Serolidse, and one species, which is my Serolis antarctica, is 

 stated to occur in 100 fathoms ofi" the Brazilian coast, and again in 1375 and 1600 fathoms 

 in the neighbourhood of the Crozets; 100 is a misprint for 400, which is the actual depth 

 at which the species was dredged. 



Two out of the four deep-sea species have a comparatively wide horizontal as well as 

 vertical distribution ; one of these, Serolis antarctica, occurred at Station 120 (675 

 fathoms), ofi" Pernambuco, and again at Stations 146 and 147 (1375 and 1600 fathoms), 

 between Prince Edward Islands and the Crozets ; the other, Serolis hromleyana, was 

 obtained at four localities between Australia and New Zealand, Station 164b (410 

 fathoms), at Stations 168 and 169, ofi" the east coast of New Zealand, in 1100 and 700 

 fathoms, and again, considerably to the south, close to the Antarctic Ice-Barrier, at Station 

 156 (1975 fathoms) ; Gerstaecker, in the work abeady alluded to, calls attention to an 

 obvious corollary from these facts (which have been already mentioned in v. AVillemoes 

 Suhm's Preliminary Eeport on the Crustacea observed during the voyage of the 

 Challenger'), namely, that these two species, as well as others which have a wide 

 distribution, are found in deeper water passing southwards from the equator to the pole ; 

 the facts in the distribution of Serolis hromleyana appear to me to furnish grounds for 

 another deduction, that the size of the individuals increases as they pass southwards and 

 into deeper water; the specimens dredged at Stations 164b and 169 (410 and 700 fathoms 

 respectively) are all small; out of the nine or ten specimens dredged at Station 168, 

 farther south and deeper water (1100 fathoms), five are of considerable size, almost twice 

 as large as those obtained at the two first-mentioned stations; finally, at Station 156, the 

 southernmost point at which the species was dredged, two specimens half again as large 

 as the largest of those from Station 168 were dredged up from 1975 fathoms. 



Serolis antarctica also agrees in these respects with Serolis hromleyana, though the 

 facts in this ease are not so strong, inasmuch as only a single specimen was dredged at 



1 Proc. Roy. Soc. Land., vol. xxiv. p. 585, 1876. 



